Have started my outdoor oven project a couple of weeks ago and have got the stand and the base constructed, but have hit a little design problem I could with some advice on. I will post my photos soon, as soon as I get over this delay!

Basically, I've built my base using a thick oak frame, in the corner of a walled patio, with a stone pillar for the front leg. On top of this is 4x 50mm thick x 600mm square concrete slabs as the base, with 100mm depth of AAC block for insulation layer (beneath the floor).

I intend to lay a thin layer of stone dust over the AAC block, with brickies sand over that, beneath the fire brick floor. The firebrick floor will be surrounded by clay bricks mortared to the concrete slabs.

My question is this:
Should I use normal brickies mortar (6:1, sand:cement) or firebrick mortar (10:6:2:3, sand:clay:cement:Lime) to mortar the bricks to the concrete slabs, that will surround firebrick floor?

The reason I ask, is that I'm not whether heat will spread down through the floor and weaken the brickies mortar or if I use refractory mortar, whether it has enough cement to be strong enough to hold the floor together, which will also have the arch buttresses on it.

I hope I haven't made this too complicated, and any advice received with thanks!

On top of this is 4x 50mm thick x 600mm square concrete slabs as the base, with 100mm depth of AAC block for insulation layer (beneath the floor).

Not familiar with AAC block's R-Value, but neither the insulation nor floor bricks require any kind of mortar at all. Simply gravity. Remember, your floor as well as your dome will expand with heat and break any kind of bond anyway.

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